Heating system, method for operating a heating system and use thereof

ABSTRACT

The invention relates to a heating system for generating and distributing thermal energy, comprising one or more circulation systems for distributing the heat, heating circuits for generating heat and at least one storage element ( 14 ). For economical storage of large amounts of heat and in order to improve the efficiency of the system, the heating system is dependent on a level of fluid and the circulation systems, e.g. for heating ( 23 - 29 ), storage connection, domestic water heating ( 26, 30 - 32 ), after-heating, heat exchange, storage collectors ( 5, 7 - 10 ), heating boiler ( 33 - 38 ), heating pumps, procurement of heat and cooling, are connected directly to the storage element ( 14 ), whereby the storage fluid is used directly by the circulation systems. Supply devices, such as filling devices ( 26, 30 ) or ( 34 ) or devices increasing the level of fluid, introduce the fluid into the circulation system before circulation and/or supply devices keep the fluid in the circulation system and/or the circulation systems dependent on the level of fluid are provided with a emergency filling device ( 31, 33 ). The invention also relates to a method for operating a heating system and to the use thereof.

The invention relates to a heating system for generating anddistributing thermal energy, the heating system comprising one or moreheating circuits for distributing the heat to heat exchangers, such asradiators and/or floor heating and/or wall heating and/or service waterheat exchangers, and/or heating circuits for the generation of heat, forexample by means of collectors and/or heating boilers and/or heat pumps,and comprising at least one reservoir.

Heating systems as defined in the introduction with circulating andstorage systems which are predominantly under superatmospheric pressureare known from the general prior art. However, heating systems of thistype have the drawback that solar circulating systems are coupled to thereservoir by means of a heat exchanger in order to allow operation to beprotected against frost by means of a water-glycol mixture, resulting inlosses and reductions in efficiency. Furthermore, the superatmosphericpressure reservoirs have to be designed with hand holes or entries orflange connections for heat exchangers or stratification tubes with acorresponding stability with respect to pressure, which places highdemands on the materials, and can only be designed in modular form withvery great difficulty.

To avoid the use of water-glycol mixtures, the publications DE 28 39 258A1, DE 195 15 580 A1 and DE 43 38 604 A1 have disclosed arrangements inwhich the solar collector is separated from the pressure system and thesolar collector is evacuated by gravity if there is a risk of frost andthe water is pumped back into the collector or into the superatmosphericpressure circulating system. Although this means that it is possible todo without a heat exchanger for the collector circulating system, it isnecessary to use superatmospheric pressure reservoirs, with thefollowing drawbacks compared to unpressurized reservoirs:

-   -   limited use of store materials (generally only steel)    -   “tested superatmospheric pressure” safety measure    -   release of excess pressure through pressure relief valves    -   expansion vessels for pressure holding    -   difficulty of access, for example for fitting stratification        tubes    -   higher demands imposed on material strength and weld seams

One further known option is to use unpressurized reservoirs withcirculating systems that are subjected to pressure. In this case,however, the heating circuit is linked via a heat exchanger in thereservoir. This likewise entails costs for the heat exchanger, pressurelosses in the heating circuit and losses of efficiency at the heatexchanger and in the circulating system.

Laid-open specification DE 196 08 405 A1 has disclosed a closed solarinstallation which comprises a pressurized store with a glass pocket.The water can flow back from the solar collector into the reservoirthrough an emptying apparatus. The solar collector can be refilled by anadditional feed pump connected in parallel with the recirculation pump.A solar collector installation of this type is only suitable for amaximum collector height of up to 7 m and even then can only be operatedwith a reduced temperature. If a greater height is required, theinstallation has to be pressurized. This in turn requires pressurereservoirs. The advantages of an open store are not available with aninstallation of this type. Moreover, it is then necessary to ensure thatthe pressure safety requirements are satisfied.

It is known from laid-open specification DE 27 53 810 A1 that a solarcollector circulating system is operated at a store, the reservoir beingclosed and the return into the gas pocket opening out in the reservoir.This arrangement has the drawback that it is impossible for there to beany temperature-dependent stratification in the reservoir. Thecirculation requires a relatively strong pump with correspondingoperating costs. The through-flow must be sufficiently strong for thepressure generated in the collector to be high enough for the water inthe collector not to boil even at low temperatures. This means strongmixing in the reservoir.

Laid-open specification DE 26 14 142 A1 has disclosed a closedcirculating system for solar installations which is provided with acompensation vessel, a return tube ending below the water level in thecompensation vessel and a return tube which can be controlled bysolenoid valve opening out in the gas region of the compensation vessel.Opening the solenoid valve allows the collector to empty out under theforce of gravity. However, to introduce heat into the reservoir, acirculating system of this type requires a heat exchanger, with theassociated drawbacks of pressure losses, efficiency losses, costs andoutlay on materials. The compensation vessel and the pump need to befitted as closely beneath the collector as possible. Since attic floorsare often also built in nowadays, this means arranging this apparatusoutside the house, with additional outlay for insulation and sealing aswell as the drawback of poor accessibility for maintenance.

A further closed circulating system with a compensation tank is knownfrom DE 196 54 037 C1. In this case, a connection from the collectorfeed to a water tank is produced via a flow-controlled three-way valve,so that the collector is emptied when the circulation is inoperative. Inthis installation too it is necessary to use a heat exchanger, with thedrawbacks listed above.

Working on the basis of a heating system in accordance with the preambleof claim 1, the invention is based on the object of designing thisheating system in such a way, while avoiding the drawbacks of the knownheating systems, that greater quantities of heat can be storedeconomically and the installation efficiency is improved. Furtherobjects are to improve the operational reliability and the protection ofthe heating system against corrosion. Furthermore, it is intended thatthere should be a greater choice of materials which can be used. Thedevelopment of further heat sources and the storage of the heat fromthese sources is intended to extend the heating system.

According to the invention, the object is achieved by the features givenin the characterizing clause of claim 1, namely by the fact that

-   -   the heating system is subject to a fluid level,    -   and that circulating systems, such as heating circulating        systems, store coupling circulating systems, service water        heating circulating systems, reheating circulating systems, heat        exchanger circulating systems, store collector circulating        systems, heating boiler circulating systems, heat pump        circulating systems, heat-obtaining circulating systems, cooling        circulating systems, are directly connected to at least one        store, so that the storage fluid is directly circulated through        the circulating systems,    -   wherein provision devices, such as filling devices, or devices        which increase the fluid level, introduce the fluid into the        circulating system before it is circulated,    -   and/or wherein retaining devices retain the fluid in the        circulating system, such as cyclical or event-controlled or        constant minimal circulation or recirculation phases when        inoperative and/or additional sealing measures for components,        such as screw connections, fittings, valves, and/or the blocking        of circulating systems while they are at a shutdown and/or        increased quality assurance for circulating system and/or        devices which increase the fluid level,    -   and/or wherein heating systems which are subject to fluid level        are equipped with an emergency provision device, such as        manually actuated or short-term operation pumps, diaphragm        vessels, gas pressure vessels, valves leading to the water mains        or domestic water system or devices which increase the fluid        level, or with a connection for an emergency provision device.

Advantageous refinements of the heating system are given in claims 2 to45.

The invention also relates to a method for operating a heating system,in particular as claimed in claims 1 to 45, which accordingly is basedon the same object as the heating system. In terms of the method, thisobject is achieved by the features given in the characterizing clause ofclaim 46, namely by virtue of the fact

-   -   that the pressure-holding is dynamic, for example that the        pressure is built up with dynamic pressure generation (5, 24),        such as a recirculation pump or a series connection of pumps or        by means of a positive displacement pump or by means of a        pressure pump, and is held by means of a device (12, 20) which        generates a back pressure, such as a valve or a turbine or an        impeller or a flow body or flow flaps or adapted lines or        nozzles or slides or a distribution device, so that a defined        part of the pressure generation manifests itself in an increase        in the pressure in the circulating system and not in an increase        in the through-flow,    -   and/or that the dynamically generated pressure energy is        recovered again, for example for pressure-holding and/or        recirculation and/or provision and/or to protect against        corrosion,    -   and/or that to empty and/or provide the fluid in a circulating        system, the fluid in the circulating system is exchanged with        the gas from an inert gas region or with air, the fluid passing        through the inert gas region and/or across a gas section via the        reservoir or returning directly to the reservoir (14) via a zone        with decelerated flow or a stratification device (16, 19),        predominantly a stratification device or zone which is already        used in some other way,    -   and/or that heating systems can empty circulating systems or        parts of circulating systems which are directly linked to the        reservoir, the fluid level of the reservoir projecting into the        region that is to be emptied,    -   and/or that heating systems, for reliable emptying, record the        fault using sensors and/or reliably ensure emptying by means of        redundant elements and/or by means of repetition operations        and/or by means of autonomous additional devices,    -   and/or that to protect against corrosion gas is collected in        and/or outside the heating system and the oxygen is bonded in        the gas,    -   and/or that to seal components, such as screw connections and/or        fittings and/or valves, a flexible hose or a shrink-fit hose        with seals is drawn over the components, the flexible hose used        predominantly being a silicone hose,    -   and/or that devices for providing and/or retaining and/or        circulating and/or pressure-holding and/or emptying fluid in        circulating systems by means of central and/or distributed        devices in a heating system act on a plurality of circulating        systems simultaneously or, by switching, act on the particular        cycle circuit independently of one another with the        abovementioned functions,    -   and/or that for venting purposes the or parts of the heating        system are dynamically pressurized, such as circulating systems        which are blocked off using valves and are pressurized with the        aid of the provision device and are vented via float-controlled        vent valves combined with a pressure relief valve,    -   and/or that in the event of the flow being broken off or in the        event of insufficient flows in circulating systems, the control        device automatically switches on provision phases or        flow-increasing phases,    -   and/or that to prevent the ingress of air circulating systems or        parts thereof can be emptied,    -   and/or that to protect against frost and/or to prevent boiling        in circulating systems, in addition to solar collector        circulating systems other external circulating systems or        circulating systems or parts thereof that are not protected        against frost, such as circulating systems for heating and        removing heat from storage compounds or storage solar collectors        or for obtaining heat or for cooling, can be emptied,    -   and/or that a layer is applied to the fluid level(s) in the        heating system, a floating layer (15), such as paraffin oil,        predominantly being used for this purpose,    -   and/or that to protect against corrosion the fluid pressure in        the heating system or in parts of the heating system is        dynamically altered.

Advantageous refinements of this method are given in claims 47 to 76.

The invention also relates to the use of devices of the heating systemin such a form that devices as described in claims 7 to 12 and 16 to 44are used for heating systems which are under superatmospheric pressureor other unpressurized or emptyable or pressure-reduced circulatingsystems.

The abovementioned claims result in the advantages described below.

In modern heating systems, for solar storage in order to avoid a highswitching rate in the heating boiler, water reservoirs are increasinglybeing used as an intermediate store if it is necessary to shut down, forexample in the case of heat pumps, for the coupling of fresh waterstations, etc. The use of unpressurized fluid heat reservoirs in theheating system improves the economics and also the functions, such aslarger heat reservoir volumes, additional internal fittings forstratification, internal fittings of sensors or for heat recovery.

Moreover, an unpressurized hot water store offers the advantage ofsaving material in the design of reservoirs of this type, since this andthe flanged connections do not have to be designed for superatmosphericpressure, and consequently in addition to materials which corrode it isalso possible to use increasingly expensive corrosion-resistantmaterials. A store of this type can also simply be welded or soldered orassembled on site, with the result that better matching to the localconditions can be achieved. Moreover, there is a greater freedom ofchoice in terms of the material which can be used for the reservoir(e.g. plastic, concrete, steel, sealed brickwork, etc.).

A modular construction of reservoirs of this type is also simplified oreven made possible for the first time. Consequently, larger reservoirscan be introduced and assembled on site.

These widened options can lead to reservoirs of lower cost, so thatlarger reservoirs can be employed for optimum utilization of the solarenergy, resulting in better boosting of the heating by means of solarenergy.

Furthermore, in the case of an unpressurized store, the accessibility isimproved. By way of example, this fact can be utilized to allowintegration of stratification systems or additional latent reservoirs.

The improved accessibility also offers benefits during maintenance, forexample it is easier to carry out repair on the stratification system,with the result that it is also possible to achieve advantages withregard to service life and/or duration of usage of the materialsemployed.

With the storage fluid used directly as heat-transfer liquid in thecirculating systems, without heat exchangers being connected in between,it is possible to achieve a high level of efficiency of the heatingsystem as a whole, firstly when obtaining the thermal energy in thesolar collector, since water has a higher heat capacity thanwater-glycol mixtures, and secondly through avoiding the heat exchangerlosses.

When the heat is released in the heating circuits, it is likewisepossible to avoid heat exchanger losses through direct recirculation ofthe storage water.

Heat exchangers, safety valves, pressure compensation vessels, storeentry access points or handholes, which are expensive in terms ofmaterials, the ability to dismantle the stratification system, ventapparatuses, can be eliminated in this unpressurized heating system.

The protection against corrosion is improved, since the oxygen whichpenetrates is not oxidized by corrosion at the components, but ratherconverted by active elements. Monitoring of the penetrated oxygen caneven give rise to intervention in the system so that unsealed locationsare eliminated.

When the circulating system is inoperative, there is inert gas in theheating system, so that nowhere is there any included penetrated air, asin a pressure system, which leads to corrosion, but rather thepenetrated oxygen can be actively converted in the inert gas tank, sincethe circulating system is then in communication with the inert gas tank.

All the corrosion-resistant measures of the heating system, such asthose mentioned above and others, mean that a longer service life of theinstallation is to be expected, thereby increasing materialproductivity.

The abovementioned advantages give rise to the question of whyunpressurized or fluid level heating systems of this type have notalready been developed earlier. The answer lies in a range of problemswhich have to be resolved.

Hitherto, it has not been possible to protect installations of this typeagainst corrosion, since unpressurized circulating systems may slip intothe subatmospheric pressure range, with the result that air can easilybe drawn in. Indeed, the very purpose of a superatmospheric pressurecirculating system is to prevent the penetration of air by means ofsuperatmospheric pressure.

The fact that it is easy for air to penetrate means that the circulationis not sufficiently operationally reliable to comply with therequirements of modern systems in order also to keep maintenance costsat a low level. In circulating systems which are under a subatmosphericpressure, the venting using automated vent devices or vent valves failsto function, since these devices would in fact promote the ingress ofair when under a subatmospheric pressure.

With collector heights, for example, of over 7 m, the subatmosphericpressure is so great that the heat-transfer medium water boils even atlow temperatures, and therefore a higher temperature yield would beimpossible on account of the disrupted circulation.

The use of high-power pumps to solve this problem is not economical onaccount of the higher operating costs and the lack of standard pumps forthe high temperature range.

The filling of unpressurized circulating systems requireshigh-performance circulation which is able to mix the stratifiedarrangement in the reservoir.

Hitherto, there has been no comprehensive solution concept for variousinstallations (e.g. different store heights or collectors fitted at avery high level).

In the text which follows, the heating system and the method foroperating a heating system are explained in more detail with referenceto the drawings, which illustrate a number of exemplary embodiments. Inthe drawing, in some cases in diagrammatic form:

FIG. 1 shows a heating system with unpressurized fluid heat reservoir

FIG. 2 shows a heating system with a fluid level above the emptyinglevel

FIG. 3 shows a filling device with a series circuit

FIG. 4 shows a filling device with domestic water system

FIG. 5 shows a filling device with reservoir tank

FIG. 6 shows a hydrogen-oxygen reactor

FIG. 7 shows an emptying device

FIG. 8 shows a store assembly with heat recovery

FIG. 9 shows a device for increasing the fluid level.

An embodiment of a heating system which is in accordance with the objectset is shown in FIG. 1. It comprises an unpressurized store (14) and aplurality of unpressurized circulating systems in various designs. Thecirculating system for the heating boiler (37) shows a simple design ofa circulating system of this type. When commissioning the installation,the circulating system is filled by the emergency filling device, inthis case a manually actuated series connection of the circulation pump(34) and a further emergency filling circulation pump (33). For thispurpose, the blocking valve (38) has to be opened by the control unit.After filling has taken place, the blocking valve (38) is closed, andthe fluid is held in the cycle circuit by means of the nonreturn valve(35) and the closed blocking valve (38), thereby preventing the ingressof air. If the circulating system were not closed, the fluid couldslowly escape from the circulating system, since the upper part of thecirculating system projects above the fluid level in the reservoir (14)and would therefore be under subatmospheric pressure. The higher thecirculating system projects upward with respect to the fluid level, thegreater the subatmospheric pressure. This subatmospheric pressure wouldcause the circulating system to suck in air and the fluid would escape,and consequently after a certain time the circulating system would nolonger be operable by means of the recirculation pump. Blocking off thecirculating system by means of the blocking valve (38, 35) keeps thecirculating system ready to operate. Therefore, if it is required forthe heating control (4) to perform recirculation, the control unit (1)merely has to open the blocking valve (38) and enable the recirculationpump, with the result that the fluid from the reservoir can becirculated with an operating energy similar to pressure systems. Theretention in blockable circulating systems can be increased stillfurther by the pressure generation for filling and/or pressure-holdingand/or for circulation remaining or being switched on during theblocking operation until the blocking operation has ended. The increasedpressure reduces or avoids the occurrence of subatmospheric pressure andthe air is kept out of the circulating system.

A further variant embodiment for retaining the fluid in the circulatingsystem is represented in the circulating system for the service waterheat exchanger (32). During commissioning, the circulating system isfilled once by means of a manually actuated emergency filling pump. Fromthis instant on, the fluid is held in the cycle circuit by virtue of ashort recirculation phase being switched on cyclically by the controlunit (1) when the cycle circuit is inoperative. This means that thecycle circuit with the recirculation pump (26) can likewise be operatedwith a low operational energy in the event of a demand for hot servicewater. To minimize the number of recirculation phases which areinitiated while the system is inoperative, these phases can also betriggered on an event-controlled basis, for example by a sensordetecting the absence of fluid, arranged at the level of the circulatingsystem in which the recirculation pump is still active. The screwconnections and fittings and valves in the cycle circuits mayadditionally also be sealed with the aid of additional sealing measures,such as flexible hoses or caps which can be pulled over them or multipleseals or seals which can be pressed on from the outside or a combinationof threaded sealing filling materials and seals or the application ofcoatings or resins, so that the operational readiness of the circulatingsystem is increased further. For sealing purposes, a flexible hose or ashrink-fit hose with seals is pulled over the screw connection and/orfittings, the flexible hose used predominantly being a silicone hose,and it being possible for a sealing material to be arranged between hoseor shrink-fit hose and screw connection or fitting.

Additional quality measures, such as applying an increased pressure tothe circulating system or screw connection securing means and/ormonitoring of the leaktightness of circulating systems, such aspressure-holding measurements, fluid level measurements in thecirculating system when it is inoperative, measurements of theintroduction of gas, also increase the readiness and installable heightof circulating systems of this type. Securing screw connections suchthat they cannot become detached, for example by means of metal plateswhich are fixed on one side and are bent onto surface, such as the screwhead face, also maintains readiness for a longer period of time.

The monitoring of the circulation by means of simple flow sensors (30,36), such as flow-actuated flaps or plates which are held in a preferredposition and deliver, for example, a magnetic signal as a function oftheir position, also protects the pump against destruction and suppliesinformation on the actuation of the emergency filling.

The use of flow sensors, including in combination with temperaturesensors, also enables the filling and circulation of the circulatingsystems to be monitored and/or subject to closed-loop and/or open-loopcontrol as a function of power, flow, volumetric through-flow and/orheat quantity. This allows increased operational readiness and heatconversion calculations and provision of heat quantities in accordancewith the heat conversion.

The use of positive displacement pumps for recirculation andpressure-holding also improves the operational readiness of the heatingsystem.

In the case of the circulating system for the heating heat exchanger(29), it is assumed that this is a complicated, extensively branchedcirculating system of increased height with respect to the fluid levelof the reservoir, with a large number of screw connections, fittings andvalves being installed. With unpressurized circulating systems of thistype, the problems arise whereby when the circulating system isinoperative, a considerable subatmospheric pressure may occur on accountof the greater height. Consequently, complete gas tightness cannot beachieved in the circulating system.

According to the invention, this problem is solved by the fact that incirculating systems of this type a provision device which, in the eventof the need for circulation, first of all fills the circulating systemwith fluid and then gradually transfers it to recirculation mode andpressure-holding mode, is used. The pressure for the filling,recirculation and pressure-holding (24) can be generated by means of apump which, with the aid of the control unit and sensors, such as theflow sensor (27), and a pressure-holding device provides open-loop orclosed-loop control of the pressure generation in accordance with thefunctions of filling, recirculation and pressure-holding.

However, for the filling device it is also possible to use alternativepressure-generating devices which are put into operation in the event ofa demand for recirculation or in the event of the circulating system notbeing ready and are then transferred to recirculation mode andpressure-holding mode, such as a diaphragm vessel (FIG. 2). In thiscase, a compressor (41), which sucks in the gas from the inert gas tank(17), for example, generates a gas pressure, so that the fluid in thediaphragm vessel (40) is displaced and, with the blocking valve (43)closed, fills the circulating system. The nonreturn valve (11) and thepressure relief valve (42) maintain the pressure while the circulatingsystem is operating, so that the diaphragm vessel (40) remains empty offluid. To empty the circulating system, it is possible to relieve thegas pressure using the pressure relief valve (42), so that the fluidruns out of the circulating system into the diaphragm vessel with theblocking valve (43) closed. As an alternative to the diaphragm vessel,it is also possible to use an upwardly facing pressure vessel. Apressurized gas storage system or a domestic water system or a pressurepump can also be used to generate the pressure. As a result, the fillingdevice can be connected to existing pressure-generating devices, therebyfurther improving the economics.

The filling device, comprising a series circuit of standardrecirculation pumps (FIG. 3) and sufficient actuation of the pumps by acontrol device, is also more economical than a large pump, since smallerpumps are produced in greater numbers. In the case of installations witha large number of circulating systems and therefore a large number ofrecirculation pumps, it may also be expedient for these recirculationpumps, in order to be filled, to be connected in series and to the cyclecircuit that is to be filled.

FIG. 4 shows a further economic form of filling. By means of thedomestic water system (46), water is passed across an oxygen-bondingunit (74), so that when the filling valve (47) is open water is passedinto the circulating system. The nonreturn valve (48) controls thedirection of filling. After the circulating system has been filled, thecontrol device closes the filling valve (47), so that the domestic watersystem is disconnected, and the circulating system can be operated.Filling with a fluid reservoir (FIG. 5), for example from a tank (50) ora fluid heat reservoir, may also be appropriate. In this case, forfilling with a filling valve (51), fluid from the reservoir can be addedto the circulating system. The reservoir can be built up by means of alevel-controlled valve (49) to the domestic water system or to the watermains or during recirculation.

If none of the filling devices mentioned above can be used, the fillingdevice may also comprise a control device and a positive displacementpump or a pressure pump.

All the filling devices can be used for emergency filling, and thevalves may be replaced by manually actuated slides and the electricallyactuated or controlled devices may be replaced by manually actuated ormanually controlled devices or devices designed for short-termoperation.

If the height of the circulating system is 10 m above the fluid level ofthe reservoir (14), a subatmospheric pressure of virtually zero prevailsin this region of the height of the circulating system. This would meana corresponding drop in the boiling point of the water. In the case ofcirculating systems which none the less have to be operated at a highertemperature and for circulating systems which project above 10 m, apressure-holding means has to supply the required pressure. The dynamicpressure-holding means comprises a pressure generation device (24) and adevice (20) which generates back pressure, such as an adjustable orcontrollable valve, turbine, impeller, flow body, flow flap, modifiedline, nozzle, slide, distribution device or the like. As a result, thepressure generation manifests itself not as an increase in flow, butrather as the desired increase in pressure in the circulating system(FIG. 1).

The pressure which is currently required can be maintained by means of acontrol device which controls the resistance of the device generatingback pressure as a function of the pressure in the circulating systemand of a desired pressure value, which is slightly above the currentboiling pressure value of the circulating system. The additional controlof the pressure generation as a function of the current flow value ofthe circulating system and the desired flow value of the requiredcirculation allows operating energy to be saved compared to fixedly setworst case settings.

Static pressure-holding when inoperative by means of blocking of thecirculating system with the aid of a closable device (20) generatingback pressure and the nonreturn valve (25) causes the pressure in thecirculating system to be held rather than having to be generated afresheach time the recirculation is interrupted briefly. Switching on thepressure generation for filling, pressure-holding and circulation duringblocking of the circulating system avoids a subatmospheric pressure inthe circulating system and keeps the air out of the circulating system.

Vent phases can be switched on in the case of extensively branchedcirculating systems that are difficult to vent. By way of example, afilling phase or a flow-increasing phase can be switched on during thecirculation if a low flow rate is measured.

A further possible venting option consists in blocking the circulatingsystem during filling, so that the pressure of the filling is held andincluded gas is discharged at the corresponding vent points with ventvalves. However, in addition to the float-controlled valve, these ventvalves also have to be combined with a pressure relief valve, so that onthe one hand the excess gas pressure in the circulating system isreduced, but on the other hand it is impossible for any air to penetratein the event of a subatmospheric pressure in the circulating system.

Since unpressurized circulating systems may slip into the subatmosphericpressure range or may even be operated at a subatmospheric pressure inorder to minimize operating costs, they are the diametric opposite ofsuperatmospheric pressure systems, since the purpose of thesuperatmospheric pressure is to keep the air out of the circulatingsystem and therefore to achieve effective protection against corrosion.

In this heating system, this problem has been solved with the aid of aninert gas tank (17), (FIG. 1, 2, 6), which is arranged above thereservoir (14) over the stratification tubes (16, 19). The inert gastank (17), which is open toward the reservoir (14) or stratificationtube (16, 19), can first of all transfer the fluid from the return ofthe circulating system (29, 9) opening out into it to the stratificationtube (19, 16), and therefore also transfer it into the reservoir, andcan secondly collect the gas from the circulating system which isentrained by the flow of fluid during filling and recirculation, andthirdly the gas can be reused and/or exploited for other purposes.

In one simple embodiment of the protection against corrosion, after theinstallation has been commissioned, the oxygen will corrode, so thatsubstantially an inert gas is to be found in the inert gas tank. Openingthe pressure-holding valve (20) and the emptying line with the emptyingvalve (28) allows the fluid to be exchanged with the inert gas when thecirculating system is inoperative, so that a subatmospheric pressure inthe circulating system is avoided and therefore protection againstcorrosion is provided. Filling the inert gas tank with a slightsuperatmospheric pressure also allows exchange to take place morequickly, and consequently only slight subatmospheric pressures areproduced during the exchange. Moreover, this means that in thegas-filled state of the circulating system, a slight superatmosphericpressure is also provided in the circulating system, so that the air canbe kept out of the circulating system.

In addition to the functions of gas collection and/or fluid gasexchange, the inert gas tank (17) can also perform and/or integratefurther functions, such as gas separation and/or oxygen bonding and/orenergy recovery and/or transfer from and into a stratification deviceand/or the stratification and/or the increasing of the fluid leveland/or the uptake of fluid from emptying and/or from the thermalexpansion of the fluid and/or the increasing of the fluid level, and aninert gas tank may also apply these functions to a plurality ofcirculating systems.

The arrangement of the functions in or at a spatial distance from thereservoir and/or spatially distributed in different tanks, and the factthat they are connected to one another and to the reservoir or to thestratification system by means of transfer devices, which can also beswitched by means of valves, facilitates spatial accommodation undervarious conditions. The gas collection in, next to or above or withinthe fluid store or fluid tank or in the circulating system also improvesthe flexibility of arrangement.

The inert gas tank (17) has a gas-permeable opening leading to thereservoir or to the stratification system in or at the reservoir orfluid tank, so that the gas bubbles from the stratification system orrecirculating system are collected in the inert gas tank. As a result,it is also possible to feed the returns from the circulating systemsinto the reservoir or directly into the stratification duct. To separategas, the tubes which open out into the reservoir or fluid tank or inertgas tank (17) and therefore the fluid which opens out are routed via agas section and via distribution devices (44), such as spray heads,spray tubes, spray plates or outlet slots, outlet holes, outlet windows,over a large area or with a fine distribution through the gas space.This makes it easy for micro- or macro-bubbles of gas which are presentin the fluid to escape from the fluid and be collected in the inert gastank, the distribution devices also being of gas-separated andfunnel-shaped design, so that macro-bubbles can escape upwards,resulting in automatic adaptation to the current flow.

The arrangement of the inert gas tank (17) in the circulating system ispreferably in the return of the circulating system or in the reservoiror fluid tank or above the reservoir or fluid tank above thestratification system or above return tubes which open out into thereservoir or fluid tank. The inert gas tank (17) or the gas-trappingapparatus or fluid-transfer apparatus may also be arranged floating,submerged or with an adjustable height or in a rigidly secured positionin or above the reservoir (14) or fluid tank or stratification system(16, 19) or the return of one of more circulating systems.

The inert gas tank (17) is of unpressurized or pressurized design, sothat it correspondingly matches the design of the reservoir or thearrangement of the inert gas tank.

By accurate pressure monitoring of the gas pressure in the inert gastank over the course of time, it is possible to recognize the lack ofleaktightness of the inert gas tank and the circulating systems, so thatsealing measures or the activation of oxygen-bonding units can beimplemented. An increase in the pressure over the course of timeindicates that subatmospheric pressures occur in the circulating system,resulting in the introduction of air. A reduction in the gas pressureindicates that there are leaks, which means that inert gas is escaping.Moreover, the pressure measurements have to be carried out under thesame conditions, such as temperature and filling levels, of thecirculating systems, or else the measurements have to be converted bycalculation to equate to identical conditions.

If complete leaktightness of the circulating system cannot be ensured,for example on account of the use of a large number of valves orgas-permeable tubes, the problem arises that carbon dioxide and oxygenare introduced. During filling and circulation in the circulatingsystems, these gases are partially dissolved in the fluid. Thedissolution of carbon dioxide in water produces carbonic acid, whichleads to corrosion of the components. Therefore, in modern heatingsystems, the inert gas used is not a nitrogen/carbon dioxide mixture,even though both gases are inert gases. This problem is solved by thefact that the return is routed via a lime filter (21), so that thecarbonic acid is neutralized.

In addition, the water is degassed again by means of the oil layer (15),predominantly comprising paraffin oil, on the reservoir water, since hotwater has a lower solubility and the heated water releases the dissolvedgas so that this gas can rise outwards through the oil layer (15)whereas it is impossible for any further gas to be taken up on accountof the water being shielded by the oil layer (15). The oil layer (15)also prevents corrosion of the edges of the reservoir in the event ofchanges in the fluid level as a result of emptying and filling of thecirculating systems. This is because the thickness of the oil layer isgreater than the change in water level. Moreover, the oil layer preventsthe evaporation of the reservoir water and allows free accessibility tothe reservoir. In addition, the oil layer can cause the gas above it todry out, since during cooling of the reservoir the cooled gas releasesmoisture which, as drops of water, can sink through the oil layer butthe oil layer also means that it is impossible for any moisturesubsequently to rise upwards. The oil layer can be applied to all thefluid levels in the heating system, for example including in the watercollection tank or inert gas tank.

The introduced oxygen is bonded in the inert gas tank (17) by anoxygen-bonding unit, so that it cannot cause corrosion at thecomponents. In a single design, this can be realized using an ironfilings filter (21) which is wetted by the return water of thecirculating system, so that the iron filings, through corrosion, bondthe oxygen in the inert gas tank in the form of iron oxide. Otherformations, such as iron materials with an increased surface area, forexample iron foams or laminated assemblies or sheet-metal coils orperforated metal sheets with spaces for water wetting, can also be usedto good effect. The activity and therefore the oxygen-bonding capacitycan be increased by partially immersing the iron filings filter in thewater and by applying an electric voltage between the iron and thewater. This arrangement then forms an electrochemical element, with theresult that the corrosion of the iron filings filter is increased. Thiseffect can also be generated by means of a metal which is further awayin the electrochemical series, such as copper, in which case the copperis likewise immersed in the water, for example by means of copper wireswhich project into the iron filings filter and are likewise wetted bythe return water. In addition to the bonding of the oxygen from the gasregion, the dissolved oxygen in the water is also bonded. Magnesium mayalso be used instead of iron.

If the level of oxygen introduced is very high, the oxygen bonding canbe enhanced by means of a combustion unit (18) which is supplied withhydrogen and bonds the oxygen to form water by means of hydrogencombustion. This can be effected using a burner flame or using ahydrogen-oxygen reactor or by means of a fuel cell.

An exemplary embodiment with a hydrogen-oxygen reaction deviceintegrated in the inert gas tank is shown in FIG. 6. Two regions areformed at the highest point in the inert gas tank (17). Thehydrogen-oxygen reaction takes place in the hydrogen-oxygen reactionregion (53). The hydrogen monitoring region (55) located beneath it isused to ensure that there is no more hydrogen in the tank than theamount desired for the defined hydrogen-oxygen reaction. The controldevice (1), by opening the hydrogen inlet valve (58) from the hydrogentank (60), admits a defined quantity of hydrogen into thehydrogen-oxygen reaction region (53). The quantity can be determined bymeans of the flow sensor (59). Since hydrogen is the lightest gas andthe hydrogen-oxygen reaction region (53) is located at the highest pointin the inert gas tank (17), the hydrogen remains in the hydrogen-oxygenreaction region (53). It is attempted to ignite the hydrogen by means ofan ignition means (54). If there is oxygen in the inert gas tank (17), ahydrogen-oxygen reaction takes place, but otherwise does not. Thecontrol device (1) attempts to effect ignition cyclically until ahydrogen-oxygen reaction is detected by means of a reaction flow sensor(57) arranged at the opening of the hydrogen-oxygen reaction region.Then, the entire process is repeated.

In the hydrogen monitoring region (55) there is a hydrogen sensor (56)which is used on an ongoing basis to detect whether there is hydrogen inthis region as a result of a fault or defect. If hydrogen is detected,the safety valve (52) is opened, so that the hydrogen can escape, andthe ignition is interrupted. As a result, the hydrogen-oxygen reactioncan never exceed the intended extent.

To determine the leaktightness of the circulating systems and of theinert gas tank, the control device (1) determines the quantity ofhydrogen consumed and references it against time or the volume of fluidconverted, and if a limit value is exceeded, messages are emitted to theseals and the reaction cycles are shortened or the hydrogen-oxygenreaction is boosted. The same effect can be achieved by means of a fuelcell, the hydrogen side of the fuel cell being supplied via a hydrogentank and the air side being evacuated by the inert gas tank, and thecurrent circuit of the fuel cell being closed. In the fuel cell, thehydrogen supply and the current circuit and the oxygen determination canbe controlled by means of the electrical energy generated, such asvoltage and current. Further protection against corrosion results fromthe method whereby the penetrated oxygen or constituents of the air and,from this, approximately the oxygen is determined, and if oxygen limitvalves are exceeded, further strategies, such as warning messagesrelating to the sealing, oxygen-bonding or making the oxygen bondingmore intensive, can be initiated.

For this purpose, it is possible to determine the quantity of theoxygen-bonding substance which is consumed, such as hydrogen or iron ormagnesium, or the quantity of substance generated in the oxygen-bondingreaction, such as water or iron oxide, or the energy generated duringthe reaction, such as flame temperature and duration of combustion, orelectric power or propagation rate and duration of the hydrogen-oxygenreaction, or, by keeping the reaction constant, a simplified value, suchas duration of the reaction or duration of the supply of oxygen-bondingsubstance or electric current which is generated.

Recording of the change in pressure in the inert gas tank (17) over thecourse of time, and from this determination of the supply of air andfrom this approximately the penetration of oxygen, also improves theprotection against corrosion.

Further increased demands imposed on unpressurized circulating systemsand therefore also better functionality are shown in FIG. 1 on the basisof the exemplary embodiment of the solar collector circulating system(9). Solar collectors may be arranged at a very high position comparedto the fluid level of the reservoir. This may require a high operationenergy for filling and pressure-holding. The use of modern pumps forpressure generation (5) with a high efficiency and the use of an energyrecovery device (12) can solve this problem. For this purpose, a smallturbine (12), which is driven by the flow of the circulating system andwhich, for example, drives an electric generator, is arranged beneaththe return in the inert gas tank. Good efficiency can be achieved bymeans of an adjustable nozzle, which on the one hand allowspressure-holding and on the other hand optimally diverts the return jetonto the turbine blades. If DC generators and motors are used for thepump, it is possible for the direct current obtained to be fed into thepump by means of a simple control circuit.

If the generator current and voltage are simultaneously used asmeasurement variable for the flow or the through-flow volume for controland monitoring purposes, a device of this type becomes economicallyviable.

However, other energy generation devices, such as compressors ormechanical transmission to the pump or other devices, may also besuitable and expedient if systems of this type are already present.

The solar collector circulating system (9), in the event of demand forrecirculation, is filled with the storage fluid by the filling device(5) by the solar control, and the fluid is fed via the return via theenergy recovery (12) and the lime/iron filings filter into thestratification tube (16) of the reservoir. Normally, the high flowvelocity and turbulence during filling would result in extensive mixingof the storage fluid, and the stratification in the reservoir would beadversely affected. Feeding the fluid from the return into thestratification tube avoids this problem and means that even duringfilling the fluid is returned to the layer at the same temperature. Thegas section which the return fluid has to cover in the inert gas tankcauses the gas bubbles to be released and collected in the inert gastank (17). When the circulating system has been filled, for exampleafter a period of time has elapsed, or in this circulating system moreappropriately when the generator has reached a defined voltage, thecirculating system is switched over to the recirculation andpressure-holding mode.

For solar circulating systems, it is expedient for the pressure holdingto be matched to the current temperature, so that the current pressurein the circulating system is produced just above the boiling pressurefor the current temperature. This saves operating energy, since thesolar circulating system (9) must be operated in a wide and hightemperature range and then only the pressure energy for the currenttemperature has to be generated. This can be generated by closed-loop oropen-loop control of the device (12) generating back pressure, such asin this case the opening of the nozzle, and simultaneous closed-loop oropen-loop control of the power of the pressure generation, so that thedesired flow is established.

Protection against frost represents a further function for circulatingsystems which are at risk from frost, on the basis of the example of thesolar collector circulating system (9). In the case of unpressurizedcirculating systems, emptying of the circulating system to protectagainst frost can be achieved in an expedient way and with littleoutlay. Compared to glycol-filled circulating systems operated with heatexchangers, as are used in current installations, the solar collectorcirculating system (9) has the advantage that the efficiency isincreased in two ways, firstly through the use of water as heat-transfermedium, which has a higher heat storage capacity than the water-glycolmixture, and therefore less liquid can be circulated for the samequantity of heat transfer, and secondly the avoidance of the heatexchanger, since the heat exchanger, unlike the unpressurized solarcirculating system (9), can never release the entire quantity of heat tothe reservoir. This results in an increased temperature in a heatexchanger circuit and therefore a greater temperature gradient at theinsulations and in the collector, and therefore increased heat losses.

The solar circulating system is emptied firstly by the return ending inthe gas space in the inert gas tank. If the pressure generationarrangements for the filling, recirculation and pressure-holding areshut down, for example by the solar control unit (3) removing the demandfor circulation on account of the lack of insolation, the gas rises outthe inert gas tank into the return, and the fluid runs into thereservoir. At the same time, the emptying valve (10) is opened, so thatthe circulating system is emptied quickly and completely and filled withthe gas pressure of the inert gas tank. This results in protectionagainst corrosion and also protection against frost for the circulatingsystem. Moreover, the solar collector can no longer boil when thereservoir has reached its heat absorption limit and insolation is stillpresent. In conventional installations with pressure circulatingsystems, a diaphragm vessel is provided for this purpose, which takes upthe pressure and liquid expansion which results from boiling. In thecase of large solar collectors or large storage volumes, the expansionvessel also has to be correspondingly large. These large expansionvessels are only produced in small numbers, making them correspondinglyexpensive. This represents an obstacle to the use of relatively largesolar installations and reservoirs to boost heating. These disadvantagesare avoided by the emptying arrangement and by unpressurized circulatingsystems, since they do not require expansion vessels and theunpressurized store can absorb the expansion volume through heating ofthe fluid.

In the case of stratification tubes, in which medium can only be fed infrom below, the opening of the return ends in the fluid region. In thiscase, for emptying purposes a further valve-controlled emptying line isrouted from the return into the gas region of the inert gas tank. It isadvantageous for the two emptying lines to be combined outside the inertgas tank, so that the inert gas tank does not require any designvariant. The separation of the gas from the fluid during filling orrecirculation is effected by the stratification tube in the case of areturn which opens out in the storage fluid. The gas rises upward in thestratification tube and is collected in the inert gas tank (17). Mixingof the reservoir by the gas bubbles is avoided, since the bubbles risein the stratification tube.

The emptying of the circulating system or return to the reservoirwithout an inert gas tank, so that the fluid gas exchange takes placewith atmosphere, is also appropriate if, for example,corrosion-resistant materials are used in the heating system.

In addition to emptying of solar circulating systems, it is alsoappropriate to be able to empty further circulating systems to protectagainst frost, for example if storage materials for storing heat arelocated outdoors and are only heated via circulating systems. In thiscase, the circulating system insulations or heat exchanger insulationsneed only be designed for solar use and can be emptied in the event oflow temperatures in order to protect against frost. The emptying ofcirculating systems for obtaining heat or cooling also bringsadvantages. If a plurality of circulating systems are to be emptied, itis economic for a central emptying device to be able to empty aplurality of circulating systems of a heating system.

The emptying of solar cycle circuits to protect against frost has nothitherto gained widespread acceptance, since the reliability of emptyingwas hitherto only incompletely resolved. Reliable emptying has to beensured, since just a single failure of emptying in the event of frostwould destroy the solar collector. There are many fault sources whichcan cause a failure to empty, such as for example the destruction ofouter insulations, mechanical defects in the emptying valve, reliabilityfaults in the electronics and sensors and mechanical elements, defectsin the electronics and sensors, software errors in the control systems.Reliable emptying can be ensured by sensors which record a fault and/orby means of redundant elements and/or by means of repetition processesand/or by means of autonomous additional devices with numerous variantembodiments, so that the economics of the methods can be configuredaccording to the complexity of the installation.

In the example shown in FIG. 1, reliability faults or defects orsoftware errors which would cause the application of pressure to beswitched on incorrectly or the emptying valve to be closed incorrectlyare counteracted by means of a linked-circuit actuating voltage. Aplurality of redundant units, such as the solar control (3), a redundantthermostat (2) and the control device (1), have to provide consent toactuation of the application of pressure (5) and to the application ofvoltage to close the emptying valve (10). Even the lack of consent fromjust one of the three devices (1, 2, 3) leads to the voltage-free stateof the application of pressure (5) and of the emptying valve (10) andtherefore to the safely emptied, frost-proof state of the solarcirculating system (9). The redundant thermostat (2) measures thetemperature in the lower range of the solar collector and is set suchthat it gives its consent at temperatures above the frost range, forexample 5° C.

Faults in the circulating system or defects in the emptying valve can bedetected by the sensor (7) recording the absence of water. The sensorwhich records the absence of water may be a simple magnetically actuatedcontact which is switched by means of a displacement-limited float afloating position, i.e. in the presence of water and a different,gravity-related position, i.e. in the absence of water. If an absence ofwater does not occur during emptying, the control device (1) starts thefilling device, repeats the emptying and tests for the absence of water.This operation can be repeated a number of times. If there is still noabsence of water, it is attempted to flush the emptying line with theemptying valve (10) a number of times, with the empting valve open, bymeans of the filling device; filling and emptying cycles of thecirculating system may also be incorporated in the mean time. Thefrequent repetition of these filling, emptying, rinsing and testing forabsence of water cycles allows sporadic malfunctions and reliabilitymalfunctions of the sensor checking for the absence of water, thecontrol device and the emptying valve, as well as releasable blockages,such as frozen sections of pipe or soiling deposits, to be bypassed oreliminated. Messages of acoustic and optical nature from these cyclescan also be used to initiate maintenance work.

The sensor checking for the absence of water can also be monitored bythe flow sensor function of the generator (12) by measuring the emptiedwater quantity, and in the event of plausibility errors a redundantemptying line with a redundant emptying valve can be opened. Theredundant thermostat (2) can also actuate the redundant emptying linewith the valve at temperatures below the frost-proofing temperature,e.g. 5° C. The redundant emptying line protects against a blockingmalfunction of the emptying line and emptying valve which cannot beeliminated by the use of pressure, heat and repetition.

The concomitant recording and listing of safety strategies which havebeen initiated and/or the failure to empty immediately makes it possibleto indicate the faulty components at an early stage and to replace thembefore damage occurs.

In installations in which the water level of the reservoir penetratesinto those parts of the circulating system which are at risk from frost,it is proposed to use a filling device with emptying feature for thecirculating system as illustrated in FIG. 2. This solar circulatingsystem (9) is separated from the reservoir by the blocking valve (43)for emptying purposes. The diaphragm vessel (40) which is acted on bypressure during filling is rendered pressure-free, by opening thepressure relief valve (42), in order for the circulating system to beemptied, and the inert gas from the diaphragm vessel can flow back intothe inert gas tank as a result of the fluid pressure in the circulatingsystem. The fluid from the circulating system flows into the diaphragmvessel and inert gas flows into the circulating system via the return ofthe latter. This provides protection against frost.

To fill the circulating system, after the pressure relief valve (42) hasclosed, inert gas is sucked out of the inert gas tank (17) by means of asmall compressor (41) and is applied to the diaphragm vessel. As aresult, the fluid is displaced back into the circulating system and theinert gas in the circulating system escapes via the return into theinert gas tank (17). With a constant power of the compressor (41), thefilling can be terminated after a defined time has elapsed, by thecompressor being switched off. Otherwise, it is also possible for sensorsignals, such as fluid levels in the diaphragm vessel or fluid levels inthe circulating system, or incoming flow volumes measured using the flowsensor (6), to be used to end the filling operation. The pressure in thediaphragm vessel is held by the nonreturn valve (11), so that thediaphragm vessel remains ready for emptying during circulation andpressure-holding. The blocking valve (43) is opened for recirculationand pressure-holding (39).

As an alternative to the compressor (41), it is also possible to useother pressure systems, such as compressed gas store, pumps or domesticwater systems with water from which the oxygen has been bonded, thewater being drained out during pressure relief using the pressure reliefvalve (42).

The diaphragm vessel (40) may also be replaced by a closedwater-receiving vessel (FIG. 7, 75) with an emptying valve (76) in theconnection to the circulating system. To keep the water-receiving vessel(75) ready for emptying, it is emptied into the reservoir by a fillingdevice. To ensure readiness for emptying, the water-receiving vessel(75) is provided with an overflow (78), so that it is always possible toempty into the water-receiving vessel, even if the filling device hasfailed or water is incorrectly flowing through the blocking valve (43).A siphon (77) in the overflow prevents the ingress of air.

In installations which have such a high fluid level that the filling ofthe circulating system can be effected with application of pressure tothe circulation and pressure-holding (39), or in which a filling device,such as a pressure pump, is installed directly in the circulatingsystem, there is no need for the compressor (41) or the pressure system,which is replaced by a tube connection and the pressure relief valve(42) is placed into the connection from the diaphragm vessel or vesselto the circulating system. In this case, the diaphragm vessel or vesselis emptied by holding the pressure relief valve (42) open and holdingthe blocking valve (43) closed at the start of filling or circulationand pressure-holding, so that the diaphragm vessel (40) or vessel isemptied. After the diaphragm vessel (40) or vessel has been emptied, thepressure relief valve (42) is closed, thereby maintaining readiness toempty the circulating system, and the blocking valve (43) is opened inorder to circulate the storage fluid. If the tank is operated inunpressurized form, an overflow of the tank ensures readiness foremptying even in the event of faults.

The strategies used to ensure emptying can also be applied to thearrangements described above.

In FIG. 2, a distribution device (44) is installed in the inert gas tankbeneath the return of the circulating system (9). This could, forexample, be a funnel which is open at the top with perforations. Thefact that it is open at the top makes it easy for macro-bubbles toescape, and the funnel shape automatically matches the flow through theperforation as a function of the through-flow volume, so that the funneldoes not overflow. By means of the perforation, the fluid is distributedinto thin flow streams, so that on the one hand it is easy formicro-bubbles of gas to escape and on the other hand the iron filingsfilter beneath it is washed bright so as to retain its ability to react.

In circulating systems which are located very high above the fluid levelof the reservoir, the dynamic pressure-holding may be rendereduneconomical by the operating costs.

To gain height, it is then proposed that the fluid level be arranged ashigh as possible. In the simplest case, this can be achieved by a storewhich is fitted at a correspondingly high level and, by way of example,extends over several stories of a building.

However, this requires a continuous construction running vertically overseveral stories of a building, which is often not available, inparticular in existing buildings.

To solve this problem, the vertical arrangement of a plurality ofunpressurized reservoirs (FIG. 7) is proposed, with the lower reservoirs(66, 67) closed and the upper store(s) (61) equipped with inert gastanks (17). Fluid exchange can be effected by means of connections (64,65, 62, 63) from and to in each case the next store up. As a result ofthe connections (64, 63) of the stratification tubes (16), the coupledreservoirs behave as one large store but do not have to be positionedvertically above one another and may also be supplemented by parallelreservoirs. This arrangement offers the advantage that the reservoirscan be distributed between rooms of a building, and the insulationlosses thereby heat these rooms.

The use of the reservoir assembly, of the connections (62, 63, 64, 65)and of the stratification device (16) as feeds and returns forcirculating systems saves outlay on piping. Therefore, returns fromcirculating systems end and/or feeds for circulating systems start inthe reservoir assembly or in the connections (62, 63, 64, 65), and/orconnections for returns from circulating systems lead out of thestratification passages (16).

By way of example in the case of reservoirs arranged in parallel in thereservoir assembly, it may also be expedient, for charging ordischarging control, to optionally produce or suppress the exchange offluid. This can be effected by shutting off the connections (62, 63, 64,65) by means of valves.

If it is impossible for any reservoirs to be set up in the rooms, it ispossible to install an arrangement as shown in FIG. 9. For this purpose,the inert gas tank (17) is arranged at a height which corresponds to thedesired fluid level and is connected to a closed store (85) via afluid-filled or gas-filled line (84). In addition, a fluid store (83)may be arranged in the line for fluid compensation during filling andemptying of circulating systems and to absorb the thermal expansion ofthe fluid. This line advantageously opens out in the stratification tube(16) or at the highest point of the reservoir, so that gas bubbles canrise up into the inert gas tank. The fluid compensation may also takeplace in the connection (84), if this latter is designed to besufficiently large, so that the fluid tank (83) can be dispensed with.Variant embodiments of the arrangement consist in the inert gas tankwith the connection and the reservoir being closed or the inert gas tank(17) having an opening being immersed in the fluid tank (83) or theconnection. It is advantageous for returns from circulating systems toend in the connection (84) and/or feeds for circulating systems to beginin the connection (84).

A further option for a device which increases the fluid level forprovision or retention in circulating systems comprises apressure-holding seal between the reservoir or fluid tank and the inertgas tank or a gas tank and a gas pressure in the tank. The gas pressureis kept static or is dynamically variable, for example by means ofpressure relief via a valve into a gas storage tank and build-up ofpressure via a compressor with intake from the gas storage tank or bymeans of a diaphragm vessel which, to build up pressure, uses thepressure from a compressor or a domestic water system or a pump, itbeing possible for the pressure to be relieved. It is possible to emptyand fill circulating systems by means of the dynamic variability of thegas pressure.

To summarize, the following options result for the device whichincreases the fluid level. This device may comprise a circulating systemand/or store assembly and/or store and/or inert gas tank (17) arrangedat an appropriate height and/or a circulating system and/or storeassembly and/or store and/or inert gas tank which is under or has beenplaced under gas pressure and/or fluid pressure.

The recovery of heat from the waste water is made economical by means ofthe unpressurized store and the arrangement of tanks or double walls ordouble floors (FIG. 8, 69). For this purpose, the control device (1)measures the temperature in the waste water feed line (71) and thetemperature in the waste water region (68). If the temperature in thefeed line is greater than in the waste water region, the waste watervalve (70) is closed. The waste water flows across the waste waterregion and exchanges its heat at the reservoir or in part itselffunctions as a store. Otherwise, the waste water valve (70) is openedand the waste water flows directly into the waste water discharge line(73). To increase the heat recovery energy, it is expedient for thetemperature to be reduced as far as possible in the lower region of thereservoir (67). This is achieved by fitting a preheating tank forservice water or by removing storage fluid for preheating in the regionof heat recovery.

Obtaining of heat from waste heat or cooling systems can also beeffected from other sources and this heat can be stored in the reservoiror fluid tank or store assembly.

For this purpose, it is expedient to obtain heat using a heat exchangeror storage heat exchanger which is located in or at the reservoir orstore assembly or fluid tank, and/or for the storage fluid to bedirectly circulated through a heat exchanger or storage heat exchanger,allowing heat to be obtained.

The heat can be obtained from waste water, from cooling systems formachines, motors, compressors, generators, electronics, photovoltaicmodules, fuel cells, chimneys, exhaust gases, floors, liquid pools ortanks, components, such as parts of buildings, boundary components,vision protection components, streets, roads, driveways, squares,transparent heat insulations. To increase the temperature, it isadvantageous for the sources for obtaining heat to be provided with alayer or layers or films which absorb light and convert it into heat orto admix one or more attachments. The fitting of a transparentattachment or attachments allows the sources for obtaining heat to beimproved further.

The fluid is only fed into the heat-obtaining exchanger if the fluid(72) supplied is warmer than the fluid which is within theheat-obtaining exchanger (69) or the surroundings of the heat-obtainingexchanger, or the storage fluid is only circulated through the heatexchanger or storage heat exchanger if storage fluid which is coolerthan the temperature of the source for obtaining heat is available.

To increase the efficiency with which heat is obtained, it isadvantageous for fluid for preheating purposes to be removed in thevicinity of the heat-obtaining exchanger or the removal of the storagefluid for obtaining heat or in the heat-obtaining layer in thereservoir, or for a preheating tank to be located in this location. Thepreheating may, for example, be used for preheating for service water orfor preheating for building walls or ceilings or buffer spaces orglasshouses.

If the protection against corrosion permits, the heat exchanger orstorage heat exchanger or preheating tank may be part of the reservoiror fluid tank or store assembly, for example a double floor or a doublefloor section or a double wall section or a double wall. Otherwise,separate tanks or heat exchangers or storage heat exchangers are to beused.

In addition to the solar collector circulating systems, it is alsopossible for other external cycle circuits or cycle circuits notprotected against frost, such as cycle circuit for heating and removingof heat from storage materials or storage solar collectors or forobtaining heat or for cooling for protection against frost and/or foravoiding boiling in circulating systems, to be emptied.

The heating system can also realize systems which, instead of the fluidheat reservoir (14), are equipped with a fluid gravel store or a storeassembly (FIG. 8), for example as described in claims 33 to 36. Heatingsystems in which the fluid heat reservoir is replaced by anunpressurized fluid tank or a fluid tank with reduced superatmosphericpressure or a fluid tank with a fluid level, such as a heat exchanger ora storage heat exchanger or an intermediate store or a fluid-receivingtank or a heating boiler, can also be realized. This is advantageous,for example, if other storage materials are used to store the heat.Combinations with the abovementioned types of store, which may likewisebe equipped with the features described in claims 33 to 36, also resultin an economic heating system of the type described in claim 1.

The proposed heating system can be operated in unpressurized form orwith a reduced superatmospheric pressure or with a superatmosphericpressure. An unpressurized heating system is desirable, since it is thenpossible to make use of all the advantages, such as saving on materialsand gas permeability of the materials. However, in the transition phaseor in existing heating systems which can only be converted tounpressurized operation at considerable cost, it is also expedient touse a heating system with a reduced superatmospheric pressure or simplywith superatmospheric pressure. In addition, the heating system can alsobe operated in subatmospheric pressure mode, in which case the corrosionprevention devices according to the invention also make a contribution.Operation with combinations of unpressurized or partially pressurized orsubatmospheric pressure in different parts of the heating system is alsopossible.

Depending on the arrangement of the heating system, it is possible forthe fluid level(s) to be located in the reservoir and/or in an inert gastank and/or in a fluid tank and/or in one or more circulating systemsand/or in a connection to the inert gas tank and/or in thestratification device and/or in fluid-receiving tanks.

By way of example, to provide the fluid on demand in the circulatingsystems, it is also expedient for the pressure-generation power or flowvelocity or the through-flow volume or the heat quantity of thecirculating system to be subject to closed-loop and/or open-loop controlas a function of the current pipe mains resistance.

For the range of functions of the heating system, it is possible forsensors, such as temperature sensors, flow or through-flow sensors (6,12, 27, 30, 36), pressure sensors, fluid level sensors and sensorsdetecting the absence or presence of fluid (7), to be arranged in thecirculating system and/or in the reservoir or fluid tank (14) and/or inand at the inert gas tank (17).

To provide, circulate, empty, hold the pressure of and retain fluid incirculating systems, it may be advantageous if a central device, such asfilling device or emergency filling device or a device for increasingthe fluid level, in a heating installation operates all the cyclecircuits simultaneously or independently of one another by beingswitched over to the particular cycle circuit.

To increase the storage density, it is advantageous for latent heatreservoirs to be integrated in the reservoir or store assembly or fluidtank or fluid gravel store.

List of Reference Symbols

-   1 control unit-   2 thermostat-   3 solar control unit-   4 heating control unit-   5 pressure generation for filling, pressure holding and circulation-   6 flow sensor-   7 sensor for detecting the absence of fluid-   8 temperature sensor-   9 solar collector-   10 emptying line with emptying valve-   11 nonreturn valve-   12 pressure holding with energy recovery-   13 iron filings structure and lime filter-   14 unpressurized fluid heat reservoir-   15 oil layer-   16 stratification tube-   17 inert gas tank-   18 oxygen-bonding unit-   19 stratification tube-   20 pressure-holding valve-   21 iron filings structure and lime filter-   22 iron filings structure and lime filter-   23 mixing valve-   24 pressure generation for filling, pressure holding and circulation-   25 nonreturn valve-   26 recirculation pump-   27 flow sensor-   28 emptying line with emptying valve-   29 heating heat exchanger-   30 flow sensor, binary-   31 emergency filling device with hand pump-   32 service water heat exchanger-   33 emergency filling with recirculation pump series connection-   34 recirculation pump-   35 nonreturn valve-   36 flow sensor, binary-   37 heating boiler-   38 blocking valve-   39 pressure generation for pressure holding and circulation-   40 diaphragm vessel-   41 pressure generation system-   42 pressure relief valve-   43 blocking valve-   44 distribution device-   45 iron filings structure and lime filter-   46 domestic water system-   47 filling valve-   48 nonreturn valve-   49 level-controlled valve-   50 so filling vessel-   51 filling valve-   52 outlet valve-   53 hydrogen-oxygen reaction region-   54 ignition means-   55 hydrogen monitoring region-   56 hydrogen sensor-   57 reaction flow sensor-   58 hydrogen inlet valve-   59 hydrogen flow sensor-   60 hydrogen tank-   61 open store-   62 store connection-   63 store connection, stratification-   64 store connection, stratification-   65 store connection-   66 closed store-   67 closed store-   68 temperature sensor, waste water region-   69 double floor, waste water region-   70 bypass for waste water region-   71 temperature sensor, waste water feed line-   72 waste water feed line-   73 waste water discharge line-   74 oxygen bonding-   75 water-receiving tank-   76 emptying valve-   77 siphon-   78 overflow-   79 connection to the reservoir-   80 gas connection to the inert gas tank-   81 circulating system connection to the inert gas tank-   82 filling device-   83 fluid tank-   84 connection, inert gas tank store-   85 fluid heat reservoir

1-77. (canceled)
 78. A heating system for generating and distributingthermal energy, comprising: at least one unpressurized fluid heatreservoir containing a storage fluid; one or more circulating systemsfor distributing heat to at least one of heat-exchanging and storingcomponents; and at least one of said circulating systems being directlyconnected to said at least one fluid heat reservoir for circulating saidstorage fluid through said circulating system.
 79. The heating systemaccording to claim 78, which comprises an inert gas tank.
 80. Theheating system according to claim 79, wherein said inert gas tank isdisposed above a level of said storage fluid in said fluid heatreservoir and is in communication, by way of a gas-permeable opening,with said fluid heat reservoir or a stratification device disposedthereat, whereby gas bubbles from said fluid heat reservoir, saidstratification device, or one of said circulating collect in said inertgas tank.
 81. The heating system according to claim 78, wherein one ormore of said circulating systems are systems for generating heat. 82.The heating system according to claim 81, wherein one or more of saidcirculating systems are solar cycle systems.
 83. The heating systemaccording to claim 78, which comprises a provision device selected fromthe group consisting of a filling device and a device for increasing afluid level in said fluid heat reservoir, said device introducing thefluid into the circulating system prior to circulating.
 84. The heatingsystem according to claim 83, which comprises a control device connectedto said provision device, wherein said provision device initiates acirculation system when circulation is required under control of saidcontrol device, and wherein a circulation mode and pressure-holding modeis set under at least one of time control, open-loop control,closed-loop control, and sensor control.
 85. The heating systemaccording to claim 78, which comprises a retention device for holdingsaid fluid in said circulating system.
 86. The heating system accordingto claim 85, wherein said retention device comprises a device forblocking and/or sealing off said circulating system.
 87. The heatingsystem according to claim 86, wherein said device for blocking and/orsealing is configured such that, when said circulating system is blockedoff for retention purposes, a generation of pressure for at least one ofpressurizing, pressure-holding, and circulating is switched on until ablocking operation has ended.
 88. The heating system according to claim78, which comprises means for holding said fluid in said circulatingsystem, said means comprising a device for cyclical or event-controlledor constant minimal circulation or said means comprising recirculationphases when inoperative.
 89. The heating system according to claim 78,which comprises emptying lines for emptying a circulating system, saidemptying lines opening into one of an inert gas tank, above said fluidheat reservoir, and to a stratification device disposed in said fluidheat reservoir.
 90. The heating system according to claim 78, whichcomprises emptying lines for emptying a circulating system, saidemptying lines being formed by feed and return lines of said circulatingsystem and being valve-controlled, said lines merging outside said inertgas tank or fluid heat reservoir or stratification device into a commonline and said common line opening into an inert gas tank or to saidfluid reservoir or to a stratification device in said fluid reservoir.91. The heating system according to claim 79, which comprises avalve-controlled emptying line for said circulating system, saidemptying line connecting to a feed of said circulating system outsidesaid inert gas tank or said fluid reservoir or a stratification device,and opening into a return ending in a gas region of said inert gas tankor above or in said fluid reservoir or above or in said stratificationdevice.
 92. The heating system according to claim 78, which comprises adevice for emptying a circulating system or a part of a circulatingsystem directly coupled to said fluid reservoir, and wherein a fluidlevel of said fluid reservoir projects into a region to be emptied. 93.The heating system according to claim 78, which comprises a device forincreasing a fluid level in the system.
 94. The heating system accordingto claim 93, which comprises a liquid-filled and/or gas-filledconnection, formed with a fluid-receiving space, disposed between aclosed reservoir and an inert gas tank disposed thereabove.
 95. Theheating system according to claim 93, wherein said device for increasingthe fluid level comprises a pressure-holding seal between said fluidreservoir and a gas-pressurized inert gas tank.
 96. The heating systemaccording to claim 93, wherein said device for increasing the fluidlevel comprises one of a reservoir and a reservoir assembly disposed ata given height.
 97. The heating system according to claim 78, whereinsaid heat fluid reservoir is a device selected from the group consistingof a storage heat exchanger, a fluid-receiving tank, a pluralitythereof, and a combination thereof.
 98. The heating system according toclaim 97, wherein said storage heat exchanger or said fluid-receivingtank forms part of a reservoir assembly.
 99. The heating systemaccording to claim 98, wherein said reservoir assembly comprises adouble base or a double wall.
 100. The heating system according to claim98, wherein said reservoir assembly comprises a plurality of reservoirsdisposed above one another, wherein lower reservoirs are closed, andsaid reservoirs are coupled to a respectively adjacent reservoir by wayof at least one connection for rising fluid and gas and by way of atleast one connection for sinking fluid.
 101. The heating systemaccording to claim 100, wherein said reservoirs are disposed a lateraloffset relative to one another, and said reservoirs are connected inparallel individually or in groups.
 102. The heating system according toclaim 100, wherein said reservoirs include stratification devicesconnected via said connection, for assuring a stratified arrangementover a plurality of said reservoirs.
 103. The heating system accordingto claim 78, which comprises a heat generator selected from a waste heatunit and a cooling systems, and wherein heat from said heat generator isstored in said reservoir.
 104. The heating system according to claim103, wherein the system is configured to feed fluid into aheat-obtaining exchanger only if the fluid is warmer than the fluid inthe heat-obtaining exchanger or than an environment of theheat-obtaining exchanger, or wherein the system is configured tocirculate the storage fluid through the heat exchanger or storage heatexchanger only if storage fluid is available at a lower temperature thana temperature at said heat generator.
 105. The heating system accordingto claim 78, which further comprises a device for dynamic pressuregeneration and a device for generating a back-pressure, said devicesbeing configured such that a defined part of the pressure generation isreflected in an increase in pressure in the circulating system but notin an increase in through-flow.
 106. The heating system according toclaim 78, which comprises a floating layer of a liquid that isimmiscible with said heat storage fluid disposed on said heat storagefluid.
 107. The heating system according to claim 106, wherein saidfloating layer is a layer of paraffin oil.
 108. A method of operating aheating system, which comprises: providing a heating system according toclaim 78; providing the heating system with a reliable emptying deviceand ensuring, by way of at least one of redundant elements, repetitionoperations, and autonomous additional devices, reliable emptying of thesystem.
 109. The method according to claim 108, which comprises assuringreliable emptying of the circulating systems by recording with a sensorat least one of an absence or presence of water and an emptied quantityof water, and initiating further safety strategies with sensor signalsissued by the sensor.
 110. The method according to claim 109, whereinthe further safety stategies are selected from the group consisting ofemptying repetitions, flushing operations, and heating operations. 111.The method according to claim 108, which comprises mounting redundant orautonomous elements for reliable emptying of the circulating systems andswitching or evaluating the elements to execute redundant functionand/or, in an event of a plausibility of an error, initiating safetystrategies.
 112. The method according to claim 111, wherein the elementsare selected from the group consisting of thermostats, temperaturesensors, and valve-controlled emptying lines.
 113. The method accordingto claims 108, which comprises assuring reliable emptying of the systemby providing and connecting in a chain a plurality of redundant systemsfor at least one of an actuation voltage for pressure-generating devicesand emptying valves or blocking valves, and consenting to a generationof pressure or non-emptying by all the redundant systems, and switchingoff a pressure generation or an emptying as soon as a consent of one ofthe redundant systems is removed.
 114. The method according to claims108, wherein the autonomous additional device comprises a dischargeapparatus, and the method comprises discharging the fluid from a part ofthe circulating system that is at risk from frost.
 115. The methodaccording to claims 114, wherein the discharge apparatus is an overflowin the fluid-receiving tank or a discharge valve with sensor control ofa fluid level.
 116. In combination with a heating system subject tosuperatmospheric pressure, the heating system according to claim 78.117. In combination with a heating system with ambient pressurecirculation systems, the heating system according to claim
 78. 118. Incombination with a heating system having a pressure-reduced circulationsystem, the heating system according to claim
 78. 119. The methodaccording to claims 108 adapted for operation of a heating systemsubject to superatmospheric pressure, ambient-pressure circulatingsystems, circulating systems with reduced superatmospheric pressure, orcirculating systems that can be emptied.